The successful operation of the Space Shuttle Program currently operated by the National Aeronautics and Space Administration has been aided by detailed preparation in anticipation of possible failures and providing corrective avenues in the eventuality of any foreseeable problems. One such provision is the development of repair techniques for replacing damaged or lost heat resistant tiles by the astronauts during the orbital portion of a space mission. The present invention, a hot melt adhesive attachment system, has been developed in conjunction with a Shuttle Work Restraint Unit for this purpose. The hot melt adhesive attachment system will releasably attach the work restraint unit to the heat resistant tiles bordering the repair site, without damaging the fragile tiles. In addition, the hot melt adhesive attachment system finds effective utility in the construction industry. Accordingly, this invention relates to a hot melt adhesive attachment pad for releasably securing an element to a surface, and in particular to an attachment pad suitable for use in the construction industry or a spatial vacuum environment.
Hot melt adhesives, commonly referred to as thermoplastic resins or thermoplastic adhesives, are well known for their ability to form a rapid, releasable bond. However, the inherent properties of hot melt adhesives have made the use of such adhesives cumbersome and messy; therefore, commercial and industrial applications are limited. Specifically, hot melt adhesives can only be applied to the surfaces of the elements to be bonded together when the adhesive is heated to a substantially liquid state. Thus, heretofore, conventional devices for applying hot melt adhesives required an expensive, intricate dispenser for dispensing quantities of the adhesive in a heated form. Alternately, the carpet seaming industry employs hot melt adhesive tapes in conjunction with specially designed heated irons.
Another device employing hot melt adhesives is the "Thermoplastic Control Complex", described in U.S. Pat. No. 4,110,506 to Cottingham et al. The thermoplastic control complex is an apparatus for releasably bonding distinct elements together and is comprised of an exothermic electrical conductor having a predetermined resistivity and selectively coated with hot melt adhesive. In operation, the complex is positioned between the elements to be joined, and the adhesive is heated to a semi-liquid state by resistive heat from the exothermic conductor. The adhesive then cools by dissipating heat to the environment, thereby solidifying and forming a strong, releasable bond. Resistive heat may be reapplied to melt the bonded adhesive and permit detachment of the elements. The thermoplastic control complex is the type of device normally used with hot melt adhesives; however, it has several objectionable features, such as: when the thermoplastic control complex is positioned between two elements such as two wooden boards which have poor heat transfer properties, the hot melt adhesive dissipates heat less rapidly, i.e., cools more slowly, thereby increasing the time needed to effect a secure bond. Such a feature is particularly objectionable when astronauts are repairing or replacing heat resistant Space Shuttle tiles during the orbital portion of a space mission. Heat transfer to the environment is extremely poor in a spatial vacuum environment, and further the Space Shuttle tiles have by design poor heat transfer properties. The astronaut normally hopes to make extravehicular repairs as rapidly as possible, but the hot melt adhesive of the thermoplastic control complex does not cool and the solidify sufficiently fast.
In addition, the thermoplastic control complex taught by Cottingham cannot be used for repeated attachment/detachment sequences. A large amount of hot melt adhesive is normally deposited on the attachment surface after detachment, thereby depleting the adhesive charge on the electrical conductor and preventing reattachment to another or the same attachment surface. Furthermore, the electrical conductor of the thermoplastic control complex normally has hard, unyielding surfaces which tend to mar or damage the attachment surface, especially a brittle, fragile attachment surface such as the surface of a heat resistant Space Shuttle tile.
Accordingly, it is an object of the present invention to provide a hot melt adhesive attachment system for releasably bonding distinct elements together.
A further object is to provide an attachment system suitable for use in construction or a spatial vacuum environment. A related object is to provide an attachment system which may be easily operated and controlled by an operator or astronaut.
Still a further object of the invention is to provide a releasable hot melt adhesive attachment system that is capable of repeated attachment/detachment sequences. A related object is to provide a hot melt adhesive attachment system which after detachment deposits a minimum amount of hot melt adhesive on the attachment surface.
Yet another object of the invention is to provide an attachment system which is lightweight, compact and durable, and may be used with a wide variety of thermoplastic adhesives.
Another object of the invention is to provide an attachment system with a soft, resilient surface to prevent damage to or marring of the attachment surface.
Still another object of the invention is to solve the problems of prior attachment systems and provide an attachment system which is not cumbersome or messy and has an active cooling system for rapid attachment.